Authorities are still working to clear dangerous explosive materials from inside Holmes' suburban Denver apartment, which Oates says was booby trapped to kill "whoever entered it," noting it would have likely been one of his officers.

A law enforcement official says federal authorities have detonated one small explosive and disarmed another.

The official says Holmes' apartment appears to have three types of explosives -- jars filled with accelerants, chemicals that would explode when mixed together and more than 30 "improvised grenades."

FBI Special agent James Yacone says that while most of the explosives have been rendered safe, "the threat has not been completely eliminated." But he says families should be allowed back into their apartments by Sunday.

Meanwhile, Holmes has been appointed a defense attorney.

Arapahoe County Sheriff Grayson Robinson says 24-year-old James Holmes was booked into the county's detention facility on Friday afternoon.

His lawyer is James O'Connor, head of the public defender's office that covers the sprawling 18th Judicial District from suburban Denver to the eastern Colorado plains. He did not immediately return a call seeking comment.

Robinson says his office is not releasing a photo of Holmes at the request of the Aurora Police Department because the case is still under investigation.

Holmes was being held without bond Saturday on suspicion of first-degree murder. He'll have an advisement hearing on Monday. Then prosecutors have 72 hours to file charges.

The University of Colorado-Denver released more information Saturday on the suspect in the Aurora movie theater shooting.

James Holmes enrolled last year in a neuroscience Ph.D. program but was withdrawing. School officials didn't provide a reason.

University spokeswoman Jacque Montgomery says first-year students must take a three-part exam at the end of the academic year to move on in the program, but she didn't know whether Holmes had taken the exam.

As part of the program, Holmes was listed as making a presentation in May about Micro DNA Biomarkers in a class named "Biological Basis of Psychiatric and Neurological Disorders."

The National Institutes of Health gives the university an annual grant for students in the school's neuroscience program. Montgomery couldn't say if Holmes received any of the money.